1. Field of the Invention
Embodiments of the present invention generally relate to processes for growing material layers, and more specifically, to processes for controlling the formation of metal silicide atop exposed regions of a substrate.
2. Description of the Related Art
Metal films (e.g., Ni, Ni—Pt, Co, Ti) react with silicon (or Si—Ge) to form silicides. Silicides are utilized in device processing for the formation of contacts (e.g., source/drain, gate). During device processing, a silicide may be formed on single-crystal silicon material associated with the device source and drain regions, and on polysilicon material associated with the device gate region. Differences in the respective silicide reaction rates generally associated with single-crystal silicon and polysilicon can result in the silicide layer having a far greater thickness above the polysilicon of the gate region than it does above the single-crystal silicon of the respective source and drain regions. Such non-uniformity in the silicide layer thickness across different regions can create numerous problems with respect to manufacturability, reliability, and device performance.
Current methods for contending with the problem of silicide thickness non-uniformity include variations of an associated Rapid Thermal Anneal (RTA) treatment. One such variation includes two main steps. During a first RTA step, sometimes called a ‘formation anneal step’, a continuous metal film (e.g., Ni, Ni—Pt, Co, Ti) previously deposited atop the polysilicon and single-crystal silicon regions of the substrate (e.g., typically Si or SiGe) is reacted at a first temperature (e.g., generally a relatively low temperature, such as between about 250° C.-350° C.) such that a predetermined amount of the metal for use in forming the final silicide layer is locked into the silicon lattice in preparation for conversion into the final desired silicide. The ‘locked-in’ or reacted portion of the metal film is relatively evenly distributed across the various silicon and single-crystal silicon regions of the substrate. In some embodiments, a thin metal cap layer is formed atop the corresponding metal film (e.g., a thin titanium (Ti) cap layer may be formed atop a metal film comprising nickel (Ni)) prior to performing the first RTA to help control the subsequent metal silicide reaction. A wet chemistry is then used to etch away any unreacted portion of the metal film remaining on the substrate surface.
During the second RTA step, sometimes called a ‘conversion anneal’ step, the substrate is subjected to a second thermal treatment, usually at a higher temperature than that associated with the first RTA step (e.g., such as between about 400°-600° C.), to convert the previously-reacted metal locked within the silicon into a final silicide layer. Because the previously-reacted metal during the first RTA step was more or less evenly distributed within the silicon lattice and because excess metal is removed during the wet etch step, the final silicide layer generated during the second RTA step has a relatively uniform thickness. However, such a process requires additional steps (such as the etch step to remove excess metal and the second RTA step) which increases cost, lowers process throughput, generates excess waste, and the like.
Thus, there is a need for an improved method for controlling metal silicide formation.